Like a lot of people I found the announcement of the season passes and what's in them or otherwise being released pretty confusing. I've spent part of this evening going through all the news articles, social media and some relevant forum topics and put together what I think is a list of all of it, but if I've missed anything please let me know. I've put the stuff explained in most detail first, but the lists under each heading are not in any order, if your favourite thing is at the bottom that doesn't mean I think it's the worst or least important, that's just where my cursor landed when adding it in.

Note on terminology:

• Activities are things to do - examples from the current game would be a zone, dungeon, PvP mode, mini-game like Tales of Tribute and so on.
• Features are ways to do things - examples from the current game are classes, skill lines, endeavours, the crown store, subclassing etc.
• Quality of Life is changes to existing features.

Each season will have a different scope and focus, only the first one is being announced in any detail now and apparently a lot of those details are still to come.

Activities

The Night Market ‘event zone’ (“dungeon adjacent activity” according to Kevin). Available for 7 weeks from April – June, and will return (temporarily) in an unspecified future season. Could eventually become permanent if we hit an undisclosed target for player activity.

• Choose 1 of 3 factions to side with
• “A gauntlet of challenging PvE encounters”
• New stories and quests (no details on how many or time to complete)

Other activities:

• Mid-sized PvP zone – still being scoped out, no details or date yet.
• Thieves Guild questline.
• Crimson Veldt trial.
• Solo dungeons (Moon Hunter Keep and March of Sacrifices.)
• The return of Sheogorath. (Putting this in this category is a guess, there are no details on what form this will take.)
• “An event” on the high seas. (Again no details on what this is.)
• “Multi-stage cooperative dynamic world events” (No details on these either, I assume something like the Writhing Wall.)

Future seasons could include a new zone, storyline or quest line.

Features

Tamriel Tomes (battle/season pass) – Combining login rewards, endeavours.

• Most stuff free for 3 months, paid versions give extra cosmetics and the ability to unlock them after the season is over.
• Weekly (5 per week) and seasonal challenges. Weekly challenges can be rerolled and will be available after that week ends. (Seasonal challenges are presumably fixed.)

Gold Coast Bazaar (new store front, like the crown store) selling previously available collectibles & some new items (100 total when Season Zero starts).

• Unique currency: Trade Bars, earned from gameplay and season passes.
• Trade bars replace event tickets and do not have a limit on how many you can hold. (Existing event tickets will be converted to trade bars.)

Other features:

• Overland Challenge Difficulty – harder, with more rewards.
• Vengeance PvP Progression System – rank up to earn new rewards and abilities.
• “Sages Vault” (no details on what this is).

Future seasons could include a new class, skill line or system.

Quality of Life

• Console updates at the same time as PC
• Dragon Knight, Warden and Sorcerer balance changes
• Two-handed skill line balance changes
• Werewolf visual changes
• Respec skills and attributes for free, within the UI
• Increased furnishing limit for some houses
• Faster riding skill training
• 15 crown store mounts and 1 new sold for gold
• Longer antiquity timers
• Account-wide outfit slots
• 30 day guild trader listings back
• Back bar gaining XP
• Vampire and Werewolf cures removed from the crown store
• Hide chest, waist, legs, hands and feet

ESO+ Changes

Adding:

• 2000 bonus tome points each month & earn them faster
• Premium+ token every 12 months (or 1 token every month with 12 unlocking 1 premium + pass?)
• Increased furnishing limit
• Increased transmute crystal limit
• Increased antiquity lead time

Losing:
Free access to DLC (and chapters when they’re re-branded DLC). Obviously this isn't listed anywhere in the advertising, but since the new events (and zones and quests if/when we get any) will be free for anyone this is no longer an ESO+ perk.

Note on paid pass unlocks: The exact wording is “should you purchase either one of the two paid versions while it is available, you can continue to unlock its free and premium rewards after the Season ends.” There is no mention of continued access to stories, zones or other activities after the end of a season, but Kevin said in a post it could happen if there’s enough interest in one.